E. coli strains have traditionally been classified as either commensal or pathogenic, and pathogenic strains are then sub-classified as intestinal or extraintestinal strains. Pathogenic E. coli are discussed in more detail in reference 1, and fall into a number of different pathotypes i.e. a group of E. coli strains that cause a common disease using a common set of virulence factors. Pathotyping of strains is a routine technique that can be performed genotypically or phenotypically. One recent genotype-based pathotyping method [2] uses a DNA microarray.
Among intestinal strains at least six well-described pathotypes are known: enteropathogenic (EPEC), enterohaemorrhagic (EHEC), enteroaggregative (EAEC), enteroinvasive (EIEC), enterotoxigenic (ETEC) and diffusely adherent (DAEC).
The extraintestinal pathogenic strains (or ‘ExPEC’ strains [3,4]) of E. coli include uropathogenic (UPEC) strains, neonatal meningitis (NMEC) strains, and septicemia-associated strains (SEPEC). ExPEC is the most common cause of urinary tract infections and one of the leading causes of neonatal meningitis and neonatal sepsis in humans, which can lead to serious complications and death. Other types of extraintestinal infections include osteomyelitis, pulmonary, intra-abdominal, soft tissue, and intravascular device-associated infections. Another ExPEC pathotype outside humans is avian pathogenic (APEC), causing extraintestinal infections in poultry.
Most previous ExPEC vaccines have been based on cell lysates or on cellular structures. SOLCOUROVAC™ includes ten different heat-killed bacteria including six ExPEC strains. URO-VAXOM™ is an oral tablet vaccine containing lyophilised bacterial lysates of 18 selected E. coli strains. Baxter Vaccines developed a UTI vaccine based on pili from 6 to 10 different strains. MedImmune developed a product called MEDI 516 based on the FimH adhesin complex. In contrast, references 5 and 6 discloses specific immunogens from ExPEC strains that can be used as the basis of defined vaccines against both NMEC and UPEC strains.
It is an object of the invention to provide further and better antigens for use in immunisation against pathogenic E. coli strains, and more particularly against intestinal pathotypes (e.g. EAEC, EIEC, EPEC and ETEC strains) as well as ExPEC pathotypes.